A door closer, generally provided to large-sized iron doors, is an automatic door closing system which allows a door to recover to its base position gradually, making use of a spring for closing at the time of opening the door.
Such door closers are divided into a rectilinear motion-type one using a piston and a rotating motion-type one using a rotating force, according to a power source for producing the accumulated recovering force at the opened door.
The above rectilinear motion-type door closer has a hydraulic cylinder installed in a body case of a laterally long shape, and a piston telescopically inserted into the hydraulic cylinder through a return spring, a rack engraved on one sidewall of the piston, and a pinion rotatably supported to a pinion shaft to be engaged with the rack at one side of the cylinder.
According to the door closer, the body case is clamped at the upper portion of a door, and the pinion shaft is securely hinged on a doorframe via a pair of hinge arms. once the door is opened, the pinion shaft rotates via the hinge arms, and its rotating force moves the piston through the rack, thus compressing the spring received in the cylinder. If loosing hold of the door, the accumulated recovering force of the return spring is controlled by the fluid and the piston returns at a predetermined speed so the pinion shaft gradually turns and the door is closed at a constant speed.
In such a door closer the hydraulic piston is rectilinearly driven by the rack and the pinion, and the door closer's overall size becomes large. It is supported onto the doorframe by a pair of the hinge arms, thus being restricted in installation. There is also much noise from several connecting parts of the hinge arms and door closer body when using the door closer for a long period of time. In the door closer the thrust load is applied to the pinion shaft, and the bearings for rotatably supporting the pinion shaft are relatively quickly worn due to the thrust load of the pinion shaft. When power is transmitted to the piston through the rack of one side, a bending load is applied to the piston in its moving direction. Thus, the piston and the cylinder are irregularly worn out.
In order to solve the above problems, a rotating motion-type door closer has been disclosed in U.S. Pat. No. 5,111,548.
The rotating motion-type door closer includes a damper having an arm fixed to a door, a rotational shaft supported at the center of the body case and formed in the body case, a pair of chambers filled with high-viscosity liquids communicating via passages of the rotational shaft, a pair of rotary blades respectively having passages with check valves on the rotational shaft and internally mounted in the pair of chambers; a stationary plate fixed to the body case; an intermediate plate engaged with the rotational shaft as to be rotatable at a predetermined angle against the return spring by the rotational shaft; a movable plate engaged with a sub case as to be rotatable together with the sub case; a plurality of rotary connectors each movably engaged with through holes formed on the intermediate plate; and an angle clutch regulating the rotation of the intermediate plate by a predetermined angle.
The adjusting arm on the sub case, as described in U.S. Pat. No. 5,274,880, has the other end hinged on the doorframe, and the inner cylinder is integrally formed with the outer cylinder coupled with the sub case, and is securely hinged on the door via the arm extending from the outer cylinder.
The conventional door closer has a pair of chambers divided by a pair of projections, and the rotation angle of the sub case is limited to 90.degree. or less. In addition, the return spring is supported between the inner and outer cylinder, thus increasing the overall size of the door closer.
If the rotation angle of the door is enlarged to 180, the door closer must be supported between the door and the doorframe via a pair of hinge arms with a hinge member due to the small rotation angle of the sub case. Therefore, it is hard to apply the conventional door closer to a two-way revolving door having no hinge arm, and reducing the overall size and weight of the door closer is not easy.
A plurality of components interconnect, which complicates the overall structure, and it is difficult to assemble them into a door closer and the assembling steps are increased to thereby lower the production yield. This also increases the overall production costs and causes frequent breakdowns.
The conventional door closer is provided to the door with a pair of the hinge arms protruding to the outside, which deteriorates the outer appearance of the door and increases the load of the door acting on the door hinge, thus preventing the door from opening smoothly, and making it difficult to mount the door closer at the door.